The present invention relates to a belt unloader and, more particularly to a belt unloader used for unloading bulk cargo such as grain, alumina, coal, limestone, gypsum, coke and copper concentrate with a belt conveyor from a hold continuously.
A belt unloader of the type described generally comprises a traveling frame which travels on a quay, a swivel base mounted on the traveling frame, a boom one end of which is mounted on the swivel base such that it is allowed to be hoisted or lowered, and a vertical carrier mounted on the boom at another end thereof such that it is allowed to swing. The vertical carrier is provided with an apparatus for taking bulk in at the lower end. The bulk is carried with it held between two belts in at least the vertical carrier.
Japanese Patent Laid-open No. Sho 63-176222 discloses a belt unloader provided with an exemplified apparatus for taking bulk. In the belt unloader, bulk is scattered upward by a rotary member called a paddle feeder and carried with it held between two opposite flat belts. The above-described apparatus is applicable for bulk cargo such as grain the bulk specific gravity of which is low, which has high fluidity in bulk and varies little in grain diameter. However, the apparatus applies too large impulse force to bulk cargo such as limestone, iron ore and ballast the bulk specific gravity of which is high because bulk is scattered upward by high-speed rotation of the paddle feeder and therefore, the apparatus is unsuitable due to noise and/or abrasion.
Japanese Patent Laid-open No. Sho 61-37628 discloses a screw unloader provided with an another apparatus for taking bulk. The apparatus does not cause the problem like above because it is designed to scrape bulk by a vertical screw conveyor. However, the apparatus has a defect that a gap of approximately 100 mm or larger is formed between the lower end of the vertical screw conveyor and the bottom of a ship or bulk cargo because a bearing and an arm for supporting it are required at the lower part of the vertical screw conveyor. As a result, bulk of at least 100 mm high is left on the bottom. Further, the above-described apparatus has another defect that if the vertical screw conveyor is used with it tilted, more bulk is left on the bottom.
Japanese Patent Laid-open No. Sho 62-201732 discloses other belt unloader. However, as described in detail later referring to drawings, this belt unloader has a disadvantage that the problem of bulk left on the bottom remains unsolved and if bulk cargo with low fluidity is carried out, efficiency of carriage is reduced. Further, if a ship fluctuates due to waves when unloading bulk cargo from the ship, an apparatus for taking bulk in may collide against the bottom of the ship and the apparatus and/or the bottom of the ship may be damaged. A wrong operation may also cause similar damage.